docs: add work log for 2026-06-15 and update DB deletion policy in README

scratch/peek_asset_pc.cjs

@@ -0,0 +1,7 @@
+const XLSX = require('xlsx');
+const workbook = XLSX.readFile('asset_pc (2026.06.15).xlsx');
+const sheetName = workbook.SheetNames[0];
+const sheet = workbook.Sheets[sheetName];
+const data = XLSX.utils.sheet_to_json(sheet, { header: 1 });
+console.log('Headers:', JSON.stringify(data[0], null, 2));
+console.log('Sample Row 1:', JSON.stringify(data[1], null, 2));